1. Field of the Invention
The present invention relates to an electric power steering apparatus. More particularly, the present invention relates to a reducer of an electric power steering apparatus that reduces rattle noise generated by a backlash due to friction and wear of a worm and a worm wheel or an impact transmitted from a road surface through a wheel and a steering shaft and enhances a steering feeling of a driver by improving the catching phenomenon and rotational resistance generated between a worm shaft and a worm shaft bearing.
2. Description of the Prior Art
FIG. 1 illustrates a conventional electric power steering apparatus. As illustrated in FIG. 1, the electric power steering apparatus 100 includes a steering wheel 101 disposed in front of a driver's seat, a steering shaft 106 connected to the steering wheel 106, a steering column 130 configured to fix the steering shaft 106 to the chassis of a vehicle, a rack/pinion mechanism 110 including a rack gear and a pinion gear and configured to convert a rotational movement of the steering shaft 106 to a linear movement, and a rack bar 112 whose opposite ends are equipped with a tie rod 122 and a knuckle arm 124 respectively.
The steering column 130 is rotated in conjunction with the steering wheel 102 as the steering shaft 106 is connected to the steering wheel 102, and an end of the steering column 130 is connected to a pinion shaft 108 by means of a pair of universal joints 104. The pinion shaft 108 is connected to the rack bar 112 through the rack/pinion mechanism 110, and opposite ends of the rack bar 112 are connected to wheels of the vehicle through the tie rods 122 and the knuckle arms 124.
An auxiliary power mechanism 140 includes a torque sensor 142 configured to detect a torque applied to the steering wheel 102 by the driver and to output an electrical signal proportional to the detected torque, an electronic control unit configured to generate a control signal based on the electrical signal transmitted from the torque sensor 142, a motor 146 configured to generate auxiliary power based on the control signal transmitted from the electronic control unit 144, and a reducer 150 including a worm 152 and a worm wheel 156 and configured to transmit the auxiliary power generated by the motor 146 to the steering shaft 106.
Thus, the electric power steering apparatus is adapted to transmit the torque generated by rotation of the steering wheel 102 to the rack bar 112 via the rack/pinion mechanism 110 and transmit the auxiliary power generated by the motor 146 to the rack bar 112 according to the generated torque.
That is, the torque generated by rotation of the steering wheel 102 and the auxiliary power generated by the motor 146 together move the rack bar 112 axially.
FIG. 2 is a sectional view illustrating a reducer of the conventional electric power steering apparatus. In the reducer of FIG. 2, a worm shaft 254 has a worm 152 and worm shaft bearings 257 are installed at opposite ends of the worm shaft 254 to support the worm shaft 254, and a plug bolt 210 is coupled to a damping coupler 240 and the worm shaft bearing 257 between them to prevent the worm shaft bearing 257 from moving in the axial direction of the worm shaft 254 and is fixed by a plug nut 220.
The worm shaft 254 is connected to the motor 146 by means of the damping coupler 240 to be rotated by driving the motor 146.
The worm wheel 156 is provided on the outer surface of the worm 152 formed on the worm shaft 154 to be enmeshed with the worm 152. The worm wheel 156 is mounted to the steering shaft 106 by which a rotational force of the steering wheel (102 of FIG. 1) manipulated by the driver is transmitted to transmit a rotational force of the worm shaft 254 generated by driving the motor 146 to the steering shaft 106.
The worm 152 and the worm wheel 156 are installed within the gear housing 260 and a motor 146 for providing a driving force to the worm shaft 254 is installed on one side of the gear housing 260, and the gear housing 260 and the motor 146 are coupled to each other by a bolt 250 using a motor cover 230.
In the above-described reducer of an electric power steering apparatus, the steering operation state of a vehicle can be stably maintained by controlling driving of a motor using an electronic control unit of a vehicle according to a vehicle operation condition and by adding a rotational force of a worm shaft generated by the motor to a rotational force of a steering wheel manipulated by the driver to transmit the resulting rotational force to a steering shaft.
However, in the reducer of the conventional electric power steering apparatus, a manufacturing error and an assembling error are accumulated at a coupling portion of a worm shaft and a motor shaft, causing a catching feeling to a bearing and increasing a rotational resistance of the worm shaft. Further, as a worm and a worm wheel are used, a gap is generated due to wear and rattle noise is generated by a backlash. Moreover, an uncomfortable feeling is caused to the driver during manipulation of the steering wheel due to rattle noise influenced by an impact transmitted from a road surface to wheels and a steering shaft.